monotheismPronunciation: /ˈmɒnə(ʊ)ˌθiːɪz(ə)m/Definition of monotheism noun [mass noun] the doctrine or belief that there is only one God. Derivatives monotheist noun & adjective monotheisticPronunciation: /-ˈɪstɪk/ adjective monotheisticallyPronunciation: /-ˈɪstɪk(ə)li/ adverb Origin: mid 17th century: from mono- 'one' + Greek theos 'god' + -ismmonotheism in other Oxford dictionaries Definition of monotheism in the US English dictionary